Index: lib/fuzzer/afl/afl_driver.cpp
===================================================================
--- lib/fuzzer/afl/afl_driver.cpp
+++ lib/fuzzer/afl/afl_driver.cpp
@@ -59,6 +59,7 @@
 #include <sys/resource.h>
 #include <sys/time.h>
 #include <unistd.h>
+#include <limits.h>
 
 #include <fstream>
 #include <iostream>
@@ -305,6 +306,19 @@
   return 0;
 }
 
+static int set_iterations(int *N, const char *arg) {
+  char *next_char;
+  long NL = strtol(arg, &next_char, 10);
+  if (NL < 1 || NL > INT_MAX || *next_char != '\0') {
+    fprintf(stderr, "WARNING: iterations invalid `%s`, default to %d\n",
+        arg, *N);
+    return -1;
+  }
+
+  *N = static_cast<int>(NL);
+  return 0;
+}
+
 int main(int argc, char **argv) {
   fprintf(stderr,
       "======================= INFO =========================\n"
@@ -331,11 +345,11 @@
 
   int N = 1000;
   if (argc == 2 && argv[1][0] == '-')
-      N = atoi(argv[1] + 1);
-  else if(argc == 2 && (N = atoi(argv[1])) > 0)
-      fprintf(stderr, "WARNING: using the deprecated call style `%s %d`\n",
-              argv[0], N);
-  else if (argc > 1)
+    set_iterations(&N, argv[1] + 1);
+  else if(argc == 2 && set_iterations(&N, argv[1]) == 0) {
+    fprintf(stderr, "WARNING: using the deprecated call style `%s %d`\n",
+        argv[0], N);
+  } else if (argc > 1)
     return ExecuteFilesOnyByOne(argc, argv);
 
   assert(N > 0);
Index: test/fuzzer/afl-driver.test
===================================================================
--- test/fuzzer/afl-driver.test
+++ test/fuzzer/afl-driver.test
@@ -27,3 +27,9 @@
 RUN: %run %t-AFLDriverTest %t.file3 %t.file4  2>&1 | FileCheck %s --check-prefix=CHECK5
 CHECK5: LLVMFuzzerTestOneInput called; Size = 3
 CHECK5: LLVMFuzzerTestOneInput called; Size = 4
+
+RUN: %run %t-AFLDriverTest < %t.file3 --1 2>&1 | FileCheck %s --check-prefix=CHECK6
+CHECK6: WARNING: iterations invalid `-1`, default to 1000
+
+RUN: %run %t-AFLDriverTest < %t.file3 -Invalid 2>&1 | FileCheck %s --check-prefix=CHECK7
+CHECK7: WARNING: iterations invalid `Invalid`, default to 1000